Periostin is an extracellular matrix protein consisting of a polypeptide of a molecular weight of about 90,000. The polypeptide chain contains a signal sequence, a cysteine-rich domain, a fourfold repeated domain, and a C-terminal domain.
Periostin was initially designated osteoblast-specific factor-2 (OSF-2) and was isolated and identified as a gene specifically expressed in the mouse osteoblast cell line MC3T3-E1 (Patent Literature 1, Non Patent Literature 1). The protein was later renamed periostin and was reported to have adhesion-promoting activity in osteoblast cells (Non Patent Literature 2).
In early studies, periostin was considered to be an extracellular matrix specifically expressed in bone tissue. However, it has been revealed that periostin is highly expressed not only in bone tissue but also at the onset of heart failure (Non Patent Literature 3, Non Patent Literature 4), aneurysm (Non Patent Literature 5), cancers (Non Patent Literature 6 to 8), preeclampsia (Non Patent Literature 9), vascular restenosis (Non Patent Literature 10 to 15), inflammatory diseases ((i) esophagitis (Non Patent Literature 16), (ii) sinusitis and asthma (Non Patent Literature 17), (iii) asthma (Non Patent Literature 18), (iv) angiogenesis (Non Patent Literature 6, Non Patent Literature 19 to 22)), etc. and that the protein is very slightly expressed in normal tissue. It has also been revealed that some periostin splice variants are expressed in osteoblasts (Non Patent Literature 1 and 2, Non Patent Literature 23, Patent Literature 2).
As to the functions of periostin, a periostin splice variant of 811 amino acids corresponding to PN-2 in FIG. 1) (Non Patent Literature 2) and a periostin splice variant of 783 amino acids (corresponding to PN-4 in FIG. 1) (Non Patent Literature 24) have been reported to have cell adhesion properties. In contrast, some periostin splice variants lack cell adhesion properties and they include a periostin splice variant of 838 amino acids (corresponding to PN-1 in FIG. 1) (Patent Literature 2) and a periostin splice variant of 810 amino acids (corresponding to PN-3 in FIG. 1) (Patent Literature 4).
As regards cancers, cancer metastasis is mediated by processes such as invasion of cancer cells from the primary tumor into blood vessels or lymph vessels, selective migration of cancer cells to metastatic organs, invasion of cancer cells from blood vessels into metastatic organs, growth of cancer cells supported by the microenvironment where metastasis occurred, and angiogenesis-associated growth of a tumor whose diameter exceeds several millimeters (Non Patent Literature 25 and 26). Among these complex processes for metastasis establishment, invasion and metastasis induced by the enhanced motility of cancer cells are very important stages (Non Patent Literature 27). Until now, it has been reported that highly metastatic cancer cells produce an autocrine motility factor by themselves to enhance their own motion (Non Patent Literature 28). Inhibitory substances against this malignant factor are expected as metastasis inhibitors, but no specific inhibitor has been found at present.
Various reports have been issued on high level expression of periostin in highly metastatic cancers (pancreatic cancer (Non Patent Literature 29), oral cancer (Non Patent Literature 21), pancreatic cancer (Non Patent Literature 30), breast cancer (Non Patent Literature 31), head and neck cancer (Non Patent Literature 32), colon cancer (Non Patent Literature 19), breast cancer (Non Patent Literature 6, 8 and 33), thymic cancer (Non Patent Literature 34 and 35), non-small cell lung cancer (Non Patent Literature 36 and 37), ovarian cancer (Non Patent Literature 38), prostate cancer (Non Patent Literature 39), liver cancer and bile duct cancer (Non Patent Literature 40), esophagus squamous cancer (Non Patent Literature 41), prostate cancer (Non Patent Literature 42), thyroid cancer (Non Patent Literature 43)). The high level expression of the transcription factor Twist in highly metastatic cancers has been reported (Non Patent Literature 44 and 45) and received attention. There has been a report showing that Twist is also located in the promoter region of periostin (Non Patent Literature 46). In addition, it has been reported that the invasion ability of the human embryonic kidney epithelial cell line 293T is enhanced when the periostin gene is introduced into the cell line (Non Patent Literature 47). It has also been reported that a periostin splice variant of 811 amino acids (corresponding to PN-2 in FIG. 1) was less expressed in various cancer cells, and introduction of the periostin gene into melanoma cells inhibited their metastasis to the lung (Non Patent Literature 48).
As regards vascular restenosis, a bare metal stent (BMS) has been widely used. Three to eight months after BMS implantation, in-stent restenosis (ISR) occurs in 10 to 40% of cases. The mechanism of ISR is considered to be principally neointimal hyperplasia associated with migration of smooth muscle cells from the tunica media of the coronary artery into the stent and subsequent proliferation of the cells (Non Patent Literature 49). To overcome the drawback, a drug-eluting stent (DES), which is a stent with the surface coated with a drug, was developed as a sirolimus-eluting stent (SES) by Sousa et al. in 1999. However, late stent thrombosis caused by DES has been reported, and accordingly a drug for safely inhibiting restenosis has been desired. Various papers have reported high level expression of periostin in vessel smooth muscle of an animal model with balloon injury-induced restenosis (Non Patent Literature 10 to 15).
As regards inflammations, antiinflammatory drugs have been clinically used and they include steroidal and non-steroidal antiinflammatory drugs for acute and chronic inflammatory diseases, and immunosuppressants and gold preparations for chronic progressive inflammatory diseases (for example, rheumatism, osteoarthritis, etc.). The main mechanism of action of non-steroidal antiinflammatory drugs is the inhibition of inflammatory mediators. The drugs provide symptomatic treatment and are effective for acute diseases, but less effective for chronic inflammatory diseases. Steroidal antiinflammatory drugs are highly effective for acute and chronic inflammatory diseases, but have been reported to concomitantly cause serious side effects. Accordingly, care should be taken when the drugs are used. Gold preparations are not applied to acute inflammation diseases, but are used for chronic rheumatism. Gold preparations have immunoregulatory activity and thus exert delayed effects. Gold preparations, however, also have been reported to cause side effects, including mucosal and cutaneous symptoms, myelosuppression, renal dysfunction and respiratory dysfunction. Accordingly, as with the case of steroidal antiinflammatory drugs, sufficient care should be taken when gold preparations are used. Some of immunosuppressants have also received attention in terms of clinical application to chronic rheumatism, but the side effects characteristic of immunosuppressants are of a concern.
Enhanced expression of periostin in inflammatory diseases has been reported (Non Patent Literature 16 to 18, 50 and 51).
Angiogenesis is closely associated with, in addition to cancers, aggravation of some diseases including diabetic retinopathy, atherosclerosis, periodontosis, scleroderma, glaucoma, age-related macular degeneration, and diabetes mellitus type II. Angiogenesis also plays pivotal roles in the onset and aggravation of rheumatoid arthritis, Kaposi sarcoma, psoriasis and Basedow disease (Non Patent Literature 52). It has been also shown that expansion of adipose tissue depends on angiogenesis, and the inhibition of angiogenesis has been reported to be effective for the prevention of obesity etc. (Non Patent Literature 53). In Alzheimer's disease, cerebral endothelial cells activated by angiogenesis secrete a precursor substrate for β-amyloid and a neurotoxic peptide that selectively kills cortical neurons, and hence the inhibition of angiogenesis has been reported to be effective for the prevention and treatment of Alzheimer's disease (Non Patent Literature 54). Based on these studies, angiogenesis inhibitors have been used to treat and prevent the above diseases in recent years, and there has been a demand for substances effective for inhibiting angiogenesis.
Angiogenesis inhibitors that have been found are angiostatin (Non Patent Literature 55 and 56); endostatin (Non Patent Literature 57); fumagillin derived from Aspergillus fumigatus and its synthetic derivative TNP-470 (Non Patent Literature 58); cytogenin (Non Patent Literature 59); synthetic chemical substances, such as metalloproteinase inhibitors, batimastat (BB-94) and marimastat (BB-2516) (Non Patent Literature 60 and 61); and monoclonal antibodies that inhibit the binding of angiogenesis factors (EGF, TGF-α, VEGF, etc.) to the corresponding receptors (Non Patent Literature 62). These substances, however, require careful consideration of the side effects, and the safety of the substances to a human body is not fully guaranteed.
Expression of periostin has been reported to be closely related to angiogenesis in the onset of cancers (Non Patent Literature 6, Non Patent Literature 19, Non Patent Literature 21 and 22). Induction of angiogenesis by periostin has been reported to be achieved through the expression of VEGF receptor-2 (Flk-1/KDR) in vascular endothelial cells (Non Patent Literature 20).
As described above, it has been indicated that periostin gene expression is related to vascular restenosis conditions, cancers, inflammations and angiogenesis conditions. Reports have also been made on an antibody relating to the inhibition of cell migration mediated by periostin (Non Patent Literature 12) and an antibody having inhibitory activity against periostin-induced cell growth (Non Patent Literature 13). However, the relation of the structure of a periostin splice variant to vascular restenosis, cancers, inflammations and angiogenesis still remains unclear.